1. Field of the Invention
The present invention relates generally to a camera lens module, and more particularly, to an optical image stabilizer for correcting images that are blurred by movement of the user's hand while a user takes a picture of a subject by means of a camera lens module mounted in a digital camera or a mobile terminal.
2. Description of the Related Art
With the increasing compactness and lightweight design of digital cameras, small photographing devices, such as mobile terminals equipped with an optical lens and an image sensor, have become more widespread.
In the case of a camera lens module mounted in a mobile terminal, where mobility is higher than that of other optical devices, image blurring becomes more frequent and intensified as a result of small vibrations and/or hand-movement occurring during image or video photographing. Photographing on the move will only become more frequent, and therefore, blurring of captured images, should be corrected in order to capture sharp images.
Despite the advent of high-resolution cameras due to advances in optical technologies, the benefits of mounting the high-resolution cameras on mobile terminals has been reduced due to image blurring caused by vibrations and hand-movement, increasing the need for an optical image stabilizer.
Presently, the image stabilization technologies may be roughly classified into two types. The first is Digital Image Stabilization (DIS), also known as Electronic Image Stabilization (EIS), which is an electronic hand-movement correction technology. This technology detects hand movement from the captured images and corrects the data stored in an image sensor or a memory. The image sensor receives the blurred images and adjusts positions and colors of the images in an electronic way or with a software application, making blur-free images.
Advantages of such an electronic hand-movement correction technology is that it is cheap in price because of the non-necessity of separate mechanical and physical structures and is easy to adopt due to few structural constraints. Disadvantages, however, are that this technology requires separate memories and/or high-performance image sensors since it corrects the images by means of software applications. Moreover, the prolonged time required to correct the blurred images decreases the photographing rate, and the limitation in removing the afterimages using applications may reduce the correction rate.
A second hand-movement correction technology includes Optical Image Stabilization (OIS). The OIS-based optical image stabilizer changes the position of an optical lens or an image sensor by detecting a user's hand movement and keeps the images formed on the image sensor stationary despite the vibrations of the photographing device.
Such an optical image stabilizer has a high manufacturing cost and requires an inconvenient amount of installation space, since a separate drive has to be installed. However, the optical image stabilizer may maintain a correction rate of over 90%, because it can remove the afterimages by forming blur-free images on the image sensor. Under the same conditions, the optical image stabilizer captures sharper images compared with the electronic image stabilizer. Therefore, the optical image stabilizer has been used more often than the electronic image stabilizer in photographing devices requiring high resolution.
Meanwhile, a technology for correcting images by shifting an optical lens is easy to mount in digital cameras having a space sufficient to install a built-in drive for driving the optical lens. However, since there are limitations in applying this technology to small digital cameras or mobile terminals having many spatial constraints, research has been conducted on improving technology for correcting hand movement by shifting the image sensor.
Since a significant driving force is needed to drive an optical lens having a certain weight, there is limited opportunity to miniaturize a driving device. Also, installing the driving device in portable photographing devices with rechargeable batteries creates further complications due to its large power consumption.
The difficulty in designing the small driving device and the rise in manufacturing costs due to the increase in number of parts are obstacles to securing a competitive price for photographing devices with an optical image stabilizer.